In the field of miniaturization there is a growing interest in manufacturing operating machines on the scale of micro-meters. Many of these miniature machines are polysilicon or other material superstructures on silicon substrates. Silicon oxide films of various stoichiometries are used as supports while building up the superstructures of such miniature machines. One of the critical steps in the manufacturing of these miniature machines involves the removal of the silicon oxide similar to the mechanical machining of excess material in making "big machine" components.
Many semiconductor device manufacturing processes require etching processes to allow for removal of one or more forms of silicon oxide in the production of the semiconductor device. One type of etching process used in the manufacture of semiconductor devices that has been conducted in the past is a wet acid etching procedure, typically involving liquid aqueous HF. The etch process involves exposure of the substrate to an aqueous HF solution followed by a wash and dry cycle to remove reactant and reaction product chemicals. However, this process is not easily adaptable to the manufacture of micro-machines. It has been difficult with the chemical etching processes previously known to achieve well defined edges on the etched surfaces. This is due to the chemical action of the wet etching which tends to etch isotopically, reducing the final feature dimensions. Wet etching is also problematic because at the completion of the etching process, thorough washing of the wafers is required to remove residual etching, cleaning agents and other contaminants. In the course of wet etching and the subsequent wash cycles, the surface tension and/or the turbulence, of the liquid HF and the wash solutions can easily destroy the superstructure by causing the superstructure to collapse on the silicon substrate as the silicon oxide support structure is removed.
Gas phase process procedures have been developed for silicon oxide etching utilizing a gaseous etchant medium. U.S. Pat. No. 4,749,440 to Blackwood et al. discloses a gas phase etching process for semiconductor substrates which has been implemented commercially. This process comprises exposing the substrate at near normal atmospheric pressure and room temperature to a continuously flowing atmosphere of reactive gas, preferably a mixture of anhydrous hydrogen fluoride gas mixed in a dry inert gas carrier together with a water vapor laden inert gas. The water vapor laden inert gas, preferably nitrogen, flows from a water vapor chamber, for mixing with the dry inert gas, preferably nitrogen, at a time prior to commencing flow of the anhydrous hydrogen fluoride gas and until the flow of hydrogen fluoride gas is terminated. In this process, it was discovered that mixing an anhydrous reactive gas with the inert gas and water vapor laden inert gas allows for repeatable, uniform and controllable etching at near ambient conditions. The procedure can be used in etching various types of silicon oxide films in the manufacture of integrated circuit chips, giving smooth reproducible surfaces on the substrate. However, a subsequent wash cycle is still required with this process to remove solid by-product contaminants such as H.sub.2 SiF.sub.6 precipitates, which are occasionally deposited on the substrate surface as a result of side reactions of this process. Thus a process, such as disclosed in U.S. Pat. No. 4,749,440, cannot by itself only be satisfactorily implemented for manufacturing micro-machine structures.
Deposition of solid by-products of the HF/SiO.sub.2 etching reaction can be reduced by substantially eliminating water vapor, but this reduces the rate of the etch reaction, making the reaction impractical for bulk removal of silicon oxide films on which a micro-machine superstructure has been built.